Asked if two cuts on the grey fleece hat had been caused by a pick axe handle, Miss Ashanti-Warner said: “I can’t accept damage to the hat was caused by the pick axe handle.”

The prosecution claim a pick axe handle and another sharper weapon, such as a claw hammer, were used in the attack and that Foster, and co defendant Jonathan Bowling, who has admitted the killing, both attacked Mr Greaves.

Foster aged 22, of Wesley Road, High Green, denies being involved although he admits being with Bowling, of Pitsmoor, at the time of the fatal attack on Christmas Eve.

Yesterday Ms Ashanti-Warner told the jury the hat was struck with such force that the plastic interior of the peak melted, due to friction caused by the blow.

Asked by Mr Waterman if a blow by a pick axe handle could have caused the plastic to melt, she said: “No, absolutely not.

“The pick axe handle couldn’t have passed through an area that small or caused the damage.

“I wouldn’t expect the pick axe handle to cause that degree of force.

She added: “The item that has caused the plastic to melt has to have passed through it, rather than just struck it and in doing so, friction has generated enough heat for that plastic to melt.